Apparatus for catalytic reforming

ABSTRACT

This disclosure relates to an apparatus for the catalytic reforming of gaseous hydrocarbon that may use steam and/or carbon dioxide as the reforming oxidant. The reforming is accomplished by passing the hydrocarbon and oxidant through a tube which is substantially uniformly heated its entire length and contains refractory preheater particles adjacent the inlet opening and catalytic particles intermediate the preheater particles and the tube outlet. Stoichiometric reforming is achieved without carbon deposition and degradation of the catalyst by employing preheater refractory and catalytic lump particles that are large relative to the size of the tube diameter and the particles have a bulk density of approximately 100 pounds per cubic foot.

United States Patent 72] Inventor Donald Beggs Toledo, Ohio [21] Appl. No. 821,582

[22] Filed May 5, 1969 [45] Patented Nov. 2, 1971 [7 3] Assignee Midland-Ross Corporation Toledo, Ohio [54] APPARATUS FOR CATALYTIC REFORMING 2 Claims, 1 Drawing Fig.

Primary Examiner.loseph Scovronek Attorneys-Peter Vrahotes and Harold F. Mensing ABSTRACT: This disclosure relates to an apparatus for the catalytic reforming of gaseous hydrocarbon that may use steam and/or carbon dioxide as the reforming oxidant. The reforming is accomplished by passing the hydrocarbon and oxidant through a tube which is substantially uniformly heated its entire length and contains refractory preheater particles adjacent the inlet opening and catalytic particles intermediate the preheater particles and the tube outlet. Stoichiometric reforming is achieved without carbon deposition and degradation of the catalyst by employing preheater refractory and catalytic lump particles that are large relative to the size of the tube diameter and the particles have a bulk density ofapproximately 100 pounds per cubic foot.

APPARATUS FOR CATALYTIC REFORMING DISCUSSION In the field of endothermic catalytic reforming of gaseous hydrocarbons, such as methane, natural gas, propane, or naphtha vapor, to produce a reformed gas containing CO and H steam is the reforming oxidant most commonly employed, and C0,, or mixtures of steam and CO are sometimes employed. The well-known reforming reactions, based on methane, are:

The catalyst used for such reforming is conventionally a packed bed of nominal r-inch to nominal 1-inch highly porous lump containing nickel, and such catalyst .ina'ddition to catalyzing the reforming reaction also tends tocatalyze the following carbon depositing reactions:

In reforming with steam and/or CO as the reforming-oxidant, it is common practice to utilize an amount of steam and/or CO considerably in excess of the stoichiometric amount in order to avoid carbon deposition in the catalyst. Carbon deposition in the catalyst pores will physically degrade the lump .into fines which will block gas flow through the catalyst bed and make the reforming commercially impractical. Reforming with a considerable excess of steam and/or produces a reformed gas containing substantial amounts of both H O vapor and CO which for many applications are undesirableoxidizing constituents.

I have discovered an apparatus for catalytic reformingthat enables stoichiometric reforming to be successfully achieved, using steam and/r CO as reforming oxidants, without .encountering carbon deposition of degradation of the catalyst.

This apparatus is shown in the drawing, having a single FIG., wherein an elevational, cross sectional view of a reforming furnace is shown that utilizes the principles of the instantinvention.

Referring now to the drawing, a reformer furnace is shown generally at having an outer steel casing 12 lined with insulating firebrick l4 backed up with block insulation 16 to form a furnace wall suitable for operation in the temperature range of 2,000 to 2,200 F. The furnace walls are equipped with a plurality of fuel fired burnerslS which fire into a combustion chamber 20 defined by the firebrick 14. The burners 18 are responsive through means (not shown) to a furnace temperature control thermocouple 22 for controlling the furnace temperature as required. A flue opening 24 is providedto ventthe spent combustion gases from the combustion chamber 20.

Positioned within the combustion chamber 20 is a vertically disposed catalyst tube 26 made of heat resisting alloy. The tube 26 is supported at its upper end by a suitable flanged connection 28 and arranged to expand at its lower end through a packing gland assembly 30.

Received within the tube 26 is a catalyst bed 31 comprising a plurality of discrete particles. The lower region of the tube 26 is filled with preheater lump particles 32. The preheater lump 32 is supported on a screen 34 removably fastened to the lower end of the tube 26.

The upper region of tube 26 is filled with catalyst lump particles 36. A gas pipe 38 is connected to the lower end of the tube 26 to admit the gas mixture to be reformed. A gas offtake pipe 40 is fastened to the upper end of the tube 26.

Gaseous hydrocarbon from a source 42 and reforming oxidant from a source 44 are suitably metered and ratioed by meters 45 and fed to a mixer 46 which is connected to the mixture'inlet 38.

In operation, a hydrocarbon gas such as methane, propane, or naphtha vapor is supplied from the hydrocarbon source 42 to the mixer 46. An oxidant such as steam or CO is supplied in substantially stoichiometric proportion, by adjustment of the meters 45, from source 44 to the mixer 46 wherein the hydrocarbon and oxidant are mixed. The gases are then fed from tube 38 into the catalyst tube 26. The burners l8 fire into the combustion chamber 20, thereby raising the temperature of the catalyst tube 26 within the range of l,800 to 2,200 F. As the catalyst tube 26 is heated, the catalyst lump 36 and preheater lump 32 are heated indirectly by radiation and conduction. As used throughout this specification and appended claims, the term catalytic is defined as having the ability to accelerate a reforming reaction between a hydrocarbon and an oxidant. The gases passing through the tube first contact the preheater lump 32 wherein the gas is raised to .the reacting temperature. After the gases are at the proper temperature, they then contact the catalyst lump 36 wherein the hydrocarbon and oxidant react with one another to form reductants such as COand H The gases then pass through the offtake pipe 40 to be used as desired.

It has been found that unexpected results are achieved if the lumpof the catalyst bed 31 are of a large size. For example, it has been found that if the catalyst-lump 36 is at least 20 percent the size of the diameter of the tube 26, a highly efficient reaction has taken place. More particularly, the hydrocarbon may be reformed with steam or C0, in substantially stoichiometric proportions, whereas in prior reformingoperations it was necessary to have a considerable excess amount of .steam or CO: -in order to avoid degradation of the catalyst lump 36. By degradation, it is meant that the catalytic lump would be destroyed by carbon which is deposited in the pores during the reaction if sufficient excess steam or CO; is not used. Although the reasons are not known exactly why the large lump prevents degradation at substantially stoichiometric proportions, it is believed that having the large lumpresults in a moreuniform temperature distribution within the tube 26. By having the lump 36 large, the individual particles are-exposed directly'toradiation emitted from the tube 26 and are thereby able to benefit directly from the source ofheat. In addition, the lump of this particular invention has a high density, thereby providing high thermal conductivity which, of course, results in greater distribution of heat throughout the bed 31. Still another feature of this catalytic bed 31 is that the surface of the lumps '32 and 36 is very irregular, thereby breaking up the streams of .gas as they pass through the tube 26 so that the streams aremore effectively distributed throughout the tube. Although the catalyst tube 26 shown and described has atubular configuratiom-it will be appreciated that other configurations may be used equally well.

In one example of a reforming furnace 10 which was constructed in accordance with the principles of the instant discovery, the tube 26 employed had an 8 inch inside diameter with a half-inch wall thickness and an overall length to provide 20 feet of effective heated length within the furnace.

The preheater lump 32 in the lower region of catalyst tube 26 is employed to preheat the mixture to'reforming'temperature prior tothe mixture contacting the catalyst lump. The preheater .lump used may be an aluminum oxide refractory material which has a98 percent to 99 percent purity alu minum oxide that has been prepared by melting aluminum oxide in an electric arc furnace, cooling, solidifying, and then crushing into-irregular shaped lumps. An example of such an aluminum oxide refractory material is Alundum. The lump size used was screened -3 inches and +2 inches for a-nominal 2. inch-to 3-inch lump size. The refractory aluminum oxide used is a very hard and relatively heavy refractory-materialhaving some porosity and is a good conductor of heat. The bulk density of the nominal2-inch to 33-inch lump is approxi mately 100 pounds per cubic foot, which is approximately twice the bulk density of conventional reforming catalyst.

Catalyst lump 36 in .the upper region of catalyst tube 26 was 2. Heat the water and salt mixture to approximately 150 F., Analysis of reformed gas: at which temperature the nickel nitrate solution is very fluid, C 451% like water. :6 2

3. Submerge the Alundum lump in the hot solution for to ,6 1:61: 10 minutes and then remove. 5 CH. 0.8%

4. Dry the lump at 350 F. for 1 hour to remove free and (by dmm'm) combined water.

5. Roast the lump at 750 F. for 1 hour to convert the nickel nitrate to nickel oxide.

6. Repeat steps 3, 4, and 5.

The above impregnation procedure results in a nickel penetration throughout the Alundum lump, as observed by Finally, tests were conducted reforming l,000 B.t.u. natural gas with steam. The following are representative gas flows to 10 the catalyst tube and gas analysis by volume of the reformed gas on a wet basis:

eye when a lump is fractured. Reforming tests were conducted new 332 in the reformer furnace l0, utilizing a bed of the preheater Analysis ofreformed gas: lump 32 extending to a height of 8 feet above the inside floor 5 C0 of the reformer furnace, and a l2-foot-high bed of the catalyst :2 1 lump 36 on top of the bed of preheater lump. Consequently, r-r,o |.2% 40 percent of the effective heated length of the tube 26 con- N, (by dlfl'erence) l.0%

tained preheater lump and the balance contained catalyst O During all tests described hereinafter, the catalyst In each of the above tests, the reformer was operated for a lube 26 withi the reform" furnace was maintained at a number of days under the indicated conditions with no signs of Perature of approximately near the bimom to a gas flow restriction occurring in the catalyst tube. After each P pp y P- run the furnace was shut down, cooled, and the preheater Tests were conducted "forming L natural 8 lump and catalyst lump were then removed from the catalyst Wiih which Oblained fmm 2 liquid storage tanks tube and inspected. The catalyst lump showed no signs of carequipped with vaporizers. The following are representative b d i i h i l d d i gas flows to the catalyst tube and gas analysis by volume of the The above gas flow rates, when reforming with either C0, reformed gas on a wet basis: or steam, are in a very practical range for good economics in 30 commercial application. It will be understood that, although Natural flow ssomh the invention has been described with reference to a single e L catalyst tube in the reformer furnace. the invention is applica- 'a s 4% ble to a plurality of such catalyst tubes within a reformer fur- H, 47.1% co, 0.3% It is understood that this description is for purposes of illus- 2;? g: tration only, and that various embodiments may be made therein without departing from the scope of the invention as set forth in the following claims.

lclaim:

40 1. A reformer furnace comprising: wall means, a generally cylindrical tube disposed within said wall means and having a gas inlet and a gas outlet, means for heating said tube to a temperature between 1,800 F. and 2,200 E, said tube containing a group of preheater-refractory particles adjacent the gas inlet,

N, (by difference) 0.7%

Next, reforming tests were conducted utilizing CO plus some water vapor in a process using off gas as the reforming oxidant. The representative volume analysis, on a wet basis, of the off gas utilized is as follows:

335 3: a group of catalytic particles located within the tube interco 293% mediate said first group of particles and said gas outlet, said H, 39.5% preheater refractory particles and said catalytic particles havcn, 0.8% ing a bulk density of approximately 100 pounds per cubic foot NI (by difference) l.3%

with said particles having a minimum dimension which is at least 20 percent the diameter of said tube, and means for feeding a mixture of hydrocarbon and oxidant to said gas inlet.

2. The furnace of claim I wherein said preheater lump parti- The following are representative gas flows to the catalyst tube and gas analysis by volume of the reformed gas on a wet has: cles occupy a length equal to approximately 40 percent of the effective heated length of said tube. Natural gas flow l5 l5 scl'h OlT-gas flow 4330 scl'h T T I 

2. The furnace of claim 1 whErein said preheater lump particles occupy a length equal to approximately 40 percent of the effective heated length of said tube. 